Why are the landmark retrieval and facial recognition literature so divergent?
Landmark retrieval has photographs of landmarks that you need to find out. Consider the degrees of freedom for this, the landmarks can many different colours (more than humans' faces) and also the colour range is all over the place (a landmark may be blue or white or red). The shapes of the various landmarks will also vary.
Now, consider face recognition problem. All humans faces look alike morphologically. If you look at the colour, it is not as varied as landmark recognition.
Because of the inherent data in both the problems, the research focuses on the diverging lines of thought. Rich descriptors are good for landmarks because the data itself is very rich and mired with variation. On the other hand, discriminative features are more desirable for face recognition because faces are more similar and less rich in variation, so differentiating between is hard.
It is the requirement of the problem that steers research in diverging directions.